Reduced power, no codes

Lckent48

Original poster
Member
Dec 4, 2011
43
Hi everybody, this one has me stumped.

Lately I've had a few times when, after a cold start, the truck has no power. Like a reduced engine power mode, but no lights and no codes. If I turn it off & restart, it runs fine. This seems to happen about once a month and the rest of the time it runs normally, good power and mileage, 15-16city & 21-23hwy. If it wasn't for this occasional blip, I'd think it was great.

Changed plugs, AC 41-103s, & cleaned throttle body about 5k miles ago and this started about 2k miles ago. Battery was disconnected while changing plugs and TB, about 2 hours total (with a time out for a beer).

Any ideas?
 

Sparky

Member
Dec 4, 2011
12,927
So acts like it is in REP but no actual "reduced power" lights?
Is it immediate lack of power or does it happen a few minutes later?
 

Lckent48

Original poster
Member
Dec 4, 2011
43
Car Gauge Pro. No current, pending or stored faults, nothing at all. No warning lights, & all appears normal, except will barely go. I'm baffled.

I happens immediately when I put in gear & try to drive. Idles normally, around 600rpm. On attempting to drive will not go over 2000 & feels like an old car trying to drive with choke full on.
 

Lckent48

Original poster
Member
Dec 4, 2011
43
Not that I've noticed. I'll give it a closer inspection. If it was a plugged cat, wouldn't the reduced power be more or less constant? This is happening about 1 or 2 times a month on a daily driver. On restart, it runs normally. Seems like a plugged cat would have a pretty constant effect, but I have no prior experience with cat.
 

mrrsm

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Oct 22, 2015
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If the Air Filter needs change out... now would be a good time to do so...and since the MAF and IAT are side by side and work in tandem to advise your TPS in concert wth the Accelerator Pedal and Throttle Body Electronics... cleaning the MAF Sensor might show good results as it measures Intake Air by Weight with help from the IAT on figuring in density by Temperature as interpreted by the PCM. 'AIR'Go... On cold days ...any confusion would make things a little sketchy with a Dirty MAF.

I like @m.mcmillen 's idea about a possible fractured Ceramic Honeycomb inside the CAT that might occasionally slip and block the passage of exhaust gasses. This can be easily diagnosed when the Engine is off and by tapping very lightly under the metal can of the CAT with a Dead Blow Hammer. If anything rattles from a rebound vibration... you will hear it as a metallic clinking or clanking. Replacing the CAT might be necessary if the performance issue becomes a safety issue from losing power and acceleration at very inconvenient times.
 
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Lckent48

Original poster
Member
Dec 4, 2011
43
Crawled under the truck & gave the cat a few taps. Didn't sound like anything inside was loose, no rattles or clinks. I'll try clean the MAF & check the filter tomorrow.
 
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Torker

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Jan 2, 2017
36
Udall,Ks
I know mine hates the warmer temps. Today was about 60 f max and it ran great.
 

Lckent48

Original poster
Member
Dec 4, 2011
43
Filter looks good, cleaned MAF. We'll see what happens. This occurs so infrequently it's hard to tell if anything is helping. I guess if it never happens again, this worked. If not, it may be a month before I know it didn't. I'll let you know.
 
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Chickenhawk

Member
Dec 6, 2011
779
It could be a mechanical fault in the transmission. It won't throw an emissions code. It could be a shift solenoid (easy fix), vehicle speed sensor or a failing sun shell. Next time it happens, see if the transmission is starting off in second or third instead of first. Shift manually and let us know what happens.

Also, it could also be a simple linkage problem. It could indicate Drive but actually be in 2. (The transmission is designed to start off in second gear in slippery conditions if you put it into 2.) If you suspect a linkage issue, check underneath. It may require a new bushing or simply disconnect the linkage and realign.
 

gmcman

Member
Dec 12, 2011
4,656
I would check your throttle body connector if you removed it when you cleaned it. Did you remove the connector by the black plastic connector or did you by chance pull on the wires?

Make sure all the wires are seated and use some electronics cleaner spray if you can....just allow the spray to dry before reinstalling.

I had a random reduced engine power episode before and was linked to a bad connection on one of the wires.
 

Lckent48

Original poster
Member
Dec 4, 2011
43
Guess I spoke too soon. Today I went out & started up the TB. Started normally, but when I put in gear & drove off, it would barely move. Put it back in neutral and it idled very rough & felt like it was going to die any second. If I unplug the MAF, it runs fine. Figured my new MAF went bad. Got it replaced under warranty and same thing.

With MAF plugged in, it will barely run, unplugged it runs fine, with a CEL, of course. Does this mean my MAF wiring is bad? Something else?
 
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mrrsm

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Using a "Wireless" Broken Wire Chase Tool would make checking the wiring a breeze... but if you had any work done for any after-market gear that required a Tech to splice in anywhere on top of the engine... looking for Brand New Electrical Tape wrappings would be the first place to start. These two videos cover the issues of diagnosing a sudden loss of power that coded for Reduced Engine Power...and the Broken Wire issue proved to be the source of the problem in the second of the two part series and he shows how that nifty Broken Wire Search Tool works:


The other items on the list to check next are the Fuel Pressure Regulator and Vacuum line connector...and if you can get close enough to do so ...make certain the EFI Connectors are on ...as the Germans say... "Guttentyte". The PCM might also become the last suspect to consider. If you had a spare, matched PCM... eliminating that item from the list of possibles would be a cinch.
 
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Lckent48

Original poster
Member
Dec 4, 2011
43
I'll work on this. The only code I'm getting, when the MAF is plugged in, is P0171, too lean. If I unplug the MAF, I get a P0113 and P0102, which go away if I plugin the MAF.
 

mrrsm

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Oct 22, 2015
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If you have the means to chart your Short Term and Long Term Fuel Trims and can post screen prints here ... they would be helpful to the Members who regularly use the Scanner Tool Readings to pinpoint whether the problem is with a sketchy O2 Sensor... a Stuck EFI or a problem with Fuel Pressure dying under load that is leaning things out during idle and acceleration. Its too bad that so many possible areas can alter the "Stoichiometric Sweet Spot" that even a brand new MAF Sensor cannot compensate for with help from the PCM.

These issues may also include a Bad PCV and Hose Leaks that could be hidden in a cracked or loosened vacuum hose or line somewhere on the engine that only a Smoke Test can reveal. Be careful not to experiment too much with running this engine at length while getting these Very Lean readings. If the temps get too high... you could damage the pistons and/or warp the cylinder head. This is definitely a problem in search of an early solution before bigger and badder mechanical things rear their ugly heads.
 

Lckent48

Original poster
Member
Dec 4, 2011
43
Going on vacation today, so all of this will have to wait for a couple of weeks. I'll get back into this when I get back.
 

Lckent48

Original poster
Member
Dec 4, 2011
43
Reporting back to wrap this up, I hope. After getting back from vacation, I went through everything I had looked at again. Eventually found 2 wires in the MAF sensor plug that were barely making connection (yellow and black w/white stipe). I'm guessing they would sometimes make contact and sometimes not. Anyway, I took the plug apart and cleaned up everything, put the wires back in, and everything seems to be fine now. The original issue happened on a very sporadic basis, so if it comes back again, I'll let you know. For now seems to be fixed.
 

Sparky

Member
Dec 4, 2011
12,927
That could certainly be it. Hope that takes care of it and if so, good reminder to always closely inspect electrical connections when dealing with weird issues, and not just the actual plug pins but the wiring connection to the plug.
 
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